1. Field of the Invention
The present invention relates to a video signal processing circuit of a comb filter arrangement for separating and extracting a luminance signal and a chrominance signal from an input video signal including the luminance signal and the chrominance signal.
2. Description of the Related Art
A general video tape recorder (referred to as a VTR hereinafter) separates a luminance signal and a chrominance signal from an input video signal including the luminance and the chrominance signal to form an FM-converted luminance signal and low-frequency converted chrominance signal and records them on a magnetic tape. In a general television signal, when a signal has a high line correlation, a luminance signal is concentrated near a spectrum of nf.sub.H, and the chrominance signal is concentrated near a spectrum of (n+1/2)f.sub.H. That is, the luminance signal and the chrominance signal are interleaved with each other by an f.sub.H /2 frequency. The VTR fully utilizes this interleaving to separate a luminance signal from a chrominance signal by a comb filter using a delay element having a delay time .tau..sub.D (.tau..sub.D =1/f.sub.H) corresponding to one horizontal (1H) period.
FIG. 1 shows a conventional video signal processing circuit for separating and extracting two types of signals from an input video signal. FIG. 2 shows signal waveforms of the main part of the circuit shown in FIG. 1. An input video signal A is simultaneously supplied to an adding circuit 32 and a subtracting circuit 33 in addition to a delay element 31. The delay element 31 delays the input video signal A including a luminance signal and a chrominance signal by a 1H period and outputs a 1H-delayed signal. This delayed output signal B is supplied to a band-pass filter (referred to as a BPF hereinafter) 34. The BPF 34 eliminates a DC component from the delayed output signal B from the delay element 31 to extract 1H-preceding chrominance signal C. The extracted 1H-preceding chrominance signal C is simultaneously supplied to the adding circuit 32 and the subtracting circuit 33. The adding circuit 32 extracts a luminance signal D by adding the original input video signal A and the 1H-preceding chrominance signal C. Meanwhile, the subtracting circuit 33 extracts chrominance signal E including a luminance signal by subtracting the 1H-preceding chrominance signal C from the original input video signal A. The chrominance signal E including the luminance signal is supplied to a BPF 35 and chrominance signal F is extracted by the BPF 35 from the chrominance signal E.
In the video signal processing circuit with such an arrangement, the output from the delay element 31 passes through the BPF 34. As a result, comb characteristics of the adding and subtracting circuits are limited to the band of the BPF 34, and the comb characteristics do not influence a low-frequency component of a luminance signal. Therefore, degradation of a vertical resolution can be prevented.
In the conventional circuit described above, however, since the signal delayed by the delay element 31 is added to or subtracted from the original input video signal, as shown in FIG. 2, chrominance signal components undesirably appear at a non-correlation portion of the luminance signal D. In addition, chrominance signal components undesirably appear at an achromatic portion in the chrominance signal F, or an amplitude of this portion of the chrominance signal is reduced into a half to be -6 dB, resulting in inconvenience. Particularly, in case of chrominance signal, upon Y/C separation in recording, if a color appears at an achromatic portion, since chrominance signal always pass through the comb filter circuit in a chrominance signal processing circuit of a VTR upon playback, a color appears at an achromatic portion. Therefore, a so-called color ghost appears to form an image having poor quality.